Adult squirrel monkeys will be cannulated bilaterally in the nucleus accumbens septi and subsequently injected intracranially via these cannulae with dopamine, apomorphine, amphetamine, norepinephrine or serotonin. The locomotor effects of these treatments will be assessed in a photocell activity cage designed for squirrel monkeys. Data acquisition and analysis will be achieved by means of a Heath LSI 11 minicomputer. Specificity of drug effects will be tested by systemic administration of appropriate receptor antagonists. Secondarily, a reaction time paradigm will be implemented to further evaluate the effects of intra-accumbens administration of dopamine.